1. Field of the Invention
The present invention relates to the desulfurization of petroleum oils and, more particularly, to the hydrodesulfurization of petroleum oil fractions having a significant sulfur content.
2. Description of the Prior Art
As known in the art, the presence of sulfur in petroleum oils and/or products thereof is highly objectionable, with this problem becoming particularly difficult due to the use of crude oils having an ever-increasing sulfur content. In general, sulfur occurs in petroleum oils as mercaptans, sulfides, disulfides, and as part of a substituted ring, of which thiophene, benzothiophene and dibenzothiophene are prototypes. Mercaptans are usually present in lower boiling fractions, i.e., naphtha, kerosene and the like. While numerous processes for removing sulfur from these lower boiling fractions have been proposed, see e.g., U.S. Pat. No. 4,062,762, to a large extent sulfur removal from the higher boiling fractions have proved to be a more difficult operation.
As to be discussed in more detail hereafter, sulfur is present in the higher boiling oil fractions as sulfides, disulfides and as part of the aforesaid ring compounds such as thiophene or benzothiophene with the removal of these compounds being not only difficult but also limiting the use of such heavy fractions as charged stocks for many operations such as cracking, hydrocracking, etc.
In this regard, in the past and perhaps to a limited extent under some present operating techniques, high molecular weight petroleum oil fractions have been processed in a coker to remove the sulfur as well as metal contaminants.
In more recent years, it has been proposed to remove sulfur from heavy oil fractions by catalytic hydrodesulfurization processes. Such hydrodesulfurization techniques are now well known in the petroleum industry with specific examples of some being disclosed, e.g., in U.S. Pat. Nos. 3,440,164; 3,464,915; 3,666,696; 4,006,076; 4,054,508; 4,089,774 and 4,126,538. To a considerable extent such known hydroprocessing technology involves the use of certain catalytic compositions and/or somewhat involved processing steps wherein the charge stock is initially separated into two or more fractions, with each fraction then being subjected to a separate desulfurizing steps. The individual products are then typically recombined.
While such known desulfurizing processes are effective for their intended function, they suffer from several disadvantages as, for example, a limit as to sulfur removal for a given catalyst, high operating cost due to involved processing steps and the like. The present invention is directed to an improvement over such known hydrosulfurization techniques.